The present disclosure relates to structures of front portions of vehicle bodies.
Vehicles each have a vehicle body having a front portion structure that is deformed into a predetermined configuration to absorb shock caused by a frontal collision of the vehicle. It is preferable that when shock caused by the frontal collision is absorbed as described above, the deceleration of the vehicle body (the load experienced by the vehicle body) reaches its peak during the early stages of the collision, and then the front portion structure is deformed such that the deceleration is relatively low and fixed. The reason for this is that the peak during the early stages induces forward inertial forces on occupants, thereby increasing the tension of each of seatbelts and reducing the distance between an air bag and a corresponding one of the occupants. In other words, a small amount of air bag deployment merely needs to be set, and therefore the air bag is less likely to injure the corresponding one of the occupants.
The shape of each of front side frames has conventionally been designed as described in Japanese Unexamined Patent Publication No. 2005-271811 to provide the above-described deceleration characteristics. Not only the shape has been designed as above, but also reinforcements have been locally placed on the front side frame, or a deformable bead has been provided on the front side frame to extend along the vehicle width, thereby changing the rigidity of a part of the front side frame in a front-to-rear direction of the vehicle.
Incidentally, one of significant measures to address needs for an improved behavior of a vehicle when driven and enhanced fuel efficiency is to reduce the vehicle body weight. However, such a countermeasure in which front side frames absorb shock as described above complicates the structure of each of the front side frames, for example, to inevitably increase the weight of the frame itself due to curving of the frame, or inevitably increase the frame weight due to the addition of the reinforcements to the frame.
In this connection, inventors of the present disclosure conducted studies to obtain intended shock absorption characteristics by cooperation of a front side frame and another extension frame located under the front side frame and extending forward. In other words, when the extension frame is utilized for the formation of the peak during the early stages, the front side frame merely needs to serve to absorb shock through axial compression, and the front side frame does not need to form a complicated shape. This helps reduce the weight of the front side frame.
Japanese Unexamined Patent Publication No. 2005-271811 describes that a suspension cross member below the front side frames include side frames extending forward of the vehicle, and the side frames are deformed to absorb shock caused by a frontal collision of the vehicle. This provision of the side frames is a countermeasure against a collision between the vehicle and an obstacle at a low level, which cannot be addressed using the front side frames, and does not allow the front side frames and the side frames below the front side frames to cooperate to obtain intended shock absorption characteristics.
When the extension frame is given a strength high enough to be resistant to a light collision to utilize the extension frame for the formation of the peak during the early stages, the extension frame is tightened against the collision load at the time of a light collision. Thus, the entire suspension cross member to which a collision load is transferred through the extension frame, and an entire member for supporting the suspension cross member need to be increased in rigidity, or the suspension cross member and the member need to be partially reinforced, resulting in the increased vehicle weight.
When, as described above, the front side frame and the extension frame cooperate to absorb shock, the extension frame needs to efficiently contribute to the formation of the peak during the early stages, and the front side frame needs to be axially compressed with reliability without being affected by the extension frame.
In short, it is an object of the present disclosure to reduce the collision load transferred through an extension frame to, for example, a suspension cross member at the time of a light collision.
It is another object of the present disclosure to obtain intended shock absorption characteristics by cooperation of a front side frame and the extension frame.
It is still another object of the present disclosure to obtain the intended shock absorption characteristics by cooperation of the front side frame and the extension frame to facilitate reducing the vehicle weight.
Yet other objects of the present disclosure are to allow the extension frame to ensure the formation of the peak during the early stages by the cooperation, and to ensure axial compression of the front side frame.